Southern Ground Hornbill Bucorvus Leadbeateri Research Articles

Update: Random time-activity budgets in captive Southern Ground Hornbill Bucorvus leadbeateri

Update: Random time-activity budgets in captive Southern Ground Hornbill Bucorvus leadbeateri

Indigenous knowledge of South African bird and rangeland ecology is effective for informing conservation science

South Africa's communal rangelands constitute ~25% of the country's land cover and are largely managed for livestock grazing. These habitats play an important role in rural livelihoods and cultural practices. Using semi-structured interviews, we documented indigenous local ecological knowledge (LEK) held by rural dwellers linked to natural resource utilisation, environmental health and cultural keystone indicator species (CKIS) in the grassland communities of southern KwaZulu-Natal, South Africa. Our main objective was to examine the ability for LEK to inform conservation management. We found that people who were heavily reliant on natural resources attained a higher LEK score, indicating a greater breadth of ecological knowledge, which in turn shaped their perceptions of environmental change. Community members confirmed the presence of conservation concern species within this area, highlighting the limitations of only using citizen science databases for conservation management, as their observations within these databases are biased towards major road routes and protected or urban areas. LEK can play an important role in identifying habitats crucial to species' persistence and delineating population trends over time. Our surveys highlighted the importance of the Southern Ground-hornbill Bucorvus leadbeateri as a CKIS that acts as an early warning system of changing weather, notably rain. However, LEK is context-specific, and some CKIS species such as the Southern Ground-hornbill have wide distribution ranges. Consequently, the cultural associations and implications differ based on local belief systems that are often defined by the language spoken and the community's geographical location. Our study demonstrated the importance of including indigenous LEK in conservation planning for threatened species and habitats and the importance of traditional family values responsible for transferring oral knowledge.

Habitat preferences of Southern Ground-hornbills in the Kruger National Park: implications for future conservation measures

Understanding how a species utilises its habitat, and the processes that give rise to its movements and patterns of space use, is critical for its conservation. Southern Ground-hornbills Bucorvus leadbeateri are listed as Endangered in South Africa, as a result of habitat loss and persecution. The National Species Recovery Plan lists reintroductions as a suitable conservation action, but highlights “understanding the exact habitat requirements of Southern Ground-hornbills” as a knowledge gap. In this study, we used tracking data from six Southern Ground-hornbill groups (a total of 37,060 GPS locations) in the Kruger National Park to investigate their seasonal home range differences and habitat preferences. We used first-passage time analysis to determine the scale at which Southern Ground-hornbills concentrate their foraging efforts and whether specific movement behaviours were linked to habitat types. We found marked differences in seasonal home ranges, with all groups showing a range contraction during the breeding season. Grassland and open woodland habitat types were used throughout the year in accordance with their availability within the territory, with grassland, open woodland and dense thicket being favoured habitats for foraging. Our habitat preference results, based on longitudinal GPS data, allowed us to determine ideal habitat ratios (grassland:open woodland:low shrubland of 1.00:6.10:0.09 ha) to assist with the selection of suitable reintroduction sites for Southern Ground-hornbills. With an increasing number of species being threatened with extinction, reintroductions into suitable habitats may be a useful conservation mitigation measure. However, our findings highlight the importance of a thorough understanding of a species’ movement and space use prior to the selection of areas for reintroduction to ensure the establishment and sustainability of these species at these sites.

Review of trial reintroductions of the long-lived, cooperative breeding Southern Ground-hornbill

SummaryReintroduction to, or reinforcement of, threatened wild populations are commonly used conservation strategies. Reintroductions of the Southern Ground-hornbill Bucorvus leadbeateri have been tested as a potential conservation tool for this vulnerable species since 1995. Forty-two individuals have been reintroduced under varying management strategies. We analysed the outcomes of these attempts to assess which factors contributed most to success or failure. The species exhibits complex social learning and hierarchy, and is long-lived, with delayed sexual maturity. Immediate survival was significantly affected by the season in which the release was done and by the quality of the released birds. The best-quality release birds were reared with wild behavioural characteristics and were well-socialised to captive conspecifics prior to being placed into managed groups (‘bush schools’), where social learning was led by an experienced, wild alpha male. Once reintroduced birds had survived their first year after release, continued wild experience and wild mentorship significantly affected their survival. Since sample sizes limited the rigour of some statistical analyses, other factors were considered that may also determine success. These quasi-experimental reintroductions revealed novel threats to the species, such as the importance of a nest to group cohesion, that harvested second-hatched chicks provide viable release birds, which essentially doubles wild productivity, and that reintroductions generate valuable civil society awareness of the plight of the species.

Report of suspected kidnapping in cooperative breeding Southern Ground-Hornbill in South Africa with consequences for conservation reintroductions

Kidnapping in avian species is a rarely observed phenomenon and warrants greater investigation. Kidnapping, reported for some cooperative breeding birds and mammals, has now been confirmed for the Southern Ground-Hornbill Bucorvus leadbeateri and has implications for management of reintroductions of neighbouring groups. A juvenile was kidnapped from a newly reintroduced group in Limpopo, South Africa. It is suggested that this kidnapping was driven by the group to weaken and destabilise a neighbouring group, rather than strengthen their own with an additional helper.

Natal dispersal in the Southern Ground Hornbill Bucorvus leadbeateri

Dispersal is of ecological and evolutionary importance for population biology because it affects a species’ ability to expand its range, to colonise new favourable habitats and to increase the likelihood of population persistence. Male birds are mostly philopatric, delaying dispersal or dispersing closer to their natal territories than females. Females tend to disperse further than their male siblings to reduce the chance of inbreeding. Dispersal in the cooperative breeding Southern Ground Hornbill Bucorvus leadbeateri is poorly understood. It is not known how far individuals disperse, or what the difference in dispersal age and distance is between males and females. We investigated dispersal events using field observations of ringed individuals within groups in a study population and resightings in surrounding areas. A total of 113 individuals from 19 groups were ringed during 2005–2015. Of these, 14 were breeding adults who never dispersed. Of the remaining 99, 27 were still present in their natal groups at the end of the study, four deaths were confirmed, 50 disappeared from their group and were never seen again (excluded from further analysis), and 18 were confirmed to have dispersed by direct observations in secondary groups. Median dispersal distance was similar for females and males (22 km and 25 km, respectively). Females dispersed younger than males (eight months post-fledging and 44 months post-fledging, respectively). One male delayed dispersal beyond nine years and all females dispersed before three years post-fledging. These data provide insights into the dispersal dynamics and dispersal propensity of this endangered species. Ways to improve data collection and the study of dispersal in this species are discussed.

Breeding success and population growth of Southern Ground Hornbills Bucorvus leadbeateri in an area supplemented with nest-boxes

SummaryThe provision of artificial nests can improve the conservation status of threatened bird species that are limited by nest-site availability. The shortage of natural cavity nesting sites is one factor limiting the population growth of the Southern Ground Hornbill Bucorvus leadbeateri. In an 1,800 km2 study area in north-eastern South Africa, 31 wooden nest-boxes were installed during 2002–2015. We investigated the relationships between nests, as well as environmental and social factors, with breeding. Generalised linear mixed models were fitted to the observational data and identified positive relationships between breeding attempts and each of home range size and the previous year’s rainfall; as well as positive relationships between breeding success (amongst the groups that attempt breeding) and each of earlier breeding, nest height and thickness of the nest cavity wall. The provision of nest-boxes increased the number of breeding groups and although breeding success also increased initially, it later declined as the density of breeding groups increased above 20 groups. Although nest-boxes alone did not increase overall breeding success, they are an effective conservation tool to enhance the population of Southern Ground Hornbills if spaced optimally, to enhance reproductive output in areas where suitable nest-sites are scarce or lacking.

The effects of weather, group size and type of nest on the timing of egg-laying in the Southern Ground-hornbill Bucorvus leadbeateri

The timing of breeding in birds has important consequences if food availability varies seasonally. Optimal timing of the most energetically demanding stages of breeding to coincide with peaks in food availability can increase breeding success. Early breeding may be challenging for females producing eggs, but generally birds initiating egg-laying early in the breeding season are more likely to succeed. Initiating egg-laying later may be less costly to females, but raising offspring after the peak in food availability becomes challenging. Balancing these costs and benefits is important for the cooperative breeding Southern Ground-hornbill Bucorvus leadbeateri (hereafter ‘Ground-hornbill’), which typically produces only a single clutch of two eggs and fledges a single chick per breeding season. A previous study found that Ground-hornbill groups that lay early in the breeding season are more likely to fledge a chick than later-breeding groups. We investigated factors associated with the timing of breeding such as group size, the type of nest used, rainfall and temperature in a study site supplemented with nest boxes. Ground-hornbills laid eggs from 9 September to 14 November and the average number of days between the first and the last laying date in a season was 48 ± 32 days (range 10–101 days). Larger groups, particularly those using natural nests compared to those using nest boxes, laid later than smaller groups. Egg-laying was delayed under hot, dry spring conditions and laying dates were earlier following above-average spring rainfall.

Habitat structure and diversity influence the nesting success of an endangered large cavity-nesting bird, the Southern Ground-hornbill

Habitat features can have a profound effect on the nesting success of birds. Savannas are often managed with predators and large herbivores as priority species, with little thought to the many bird species that management decisions could affect. Using a data set spanning seven breeding seasons, we examined how nesting success of Southern Ground-hornbills (SGHs) Bucorvus leadbeateri in the Kruger National Park varied as a result of various environmental and habitat factors within a radius of 3 km surrounding the nest site. Identifying which factors affect nesting success will allow for targeted management efforts to ensure the long-term survival of SGHs both within and outside of protected areas. Habitat structure and diversity of the vegetation surrounding the nest were the most influential factors on SGH nesting success. SGHs require open grassy areas for foraging and areas with large trees for nesting. Savanna habitat drivers such as elephants and fire should be managed to ensure that sufficient large trees are able to establish in the landscape and to control for bush encroachment. This is especially important in areas earmarked for SGH reintroductions. Nest sites of SGHs should be monitored to mitigate any structural changes in the habitat surrounding the nests. Nests should be modified or artificial nest sites provided, where nests have been damaged or lost, to ensure the continued presence of these birds in African savannas.Conservation implications: Habitat structure and diversity surrounding Southern Groundhornbill nests has a significant impact on their nesting success. This highlights the importance of monitoring vegetation change in savanna habitats where they occur. Management of savanna areas should take factors that influence bush encroachment, such as fire and elephants, into account to ensure the long-term persistence of these birds.

Nest temperature fluctuations in a cavity nester, the southern ground-hornbill

Southern ground-hornbills Bucorvus leadbeateri inhabit savanna and bushveld regions of South Africa. They nest in the austral summer, which coincides with the wet season and hottest daytime temperatures in the region. They are secondary cavity nesters and typically nest in large cavities in trees, cliffs and earth banks, but readily use artificial nest boxes. Southern ground-hornbills are listed as Endangered in South Africa, with reintroductions into suitable areas highlighted as a viable conservation intervention for the species. Nest microclimate, and the possible implications this may have for the breeding biology of southern ground-hornbills, have never been investigated. We used temperature dataloggers to record nest cavity temperature and ambient temperature for one artificial and 11 natural southern ground-hornbill tree cavity nests combined, spanning two breeding seasons. Mean hourly nest temperature, as well as mean minimum and mean maximum nest temperature, differed significantly between southern ground-hornbill nests in both breeding seasons. Mean nest temperature also differed significantly from mean ambient temperature for both seasons. Natural nest cavities provided a buffer against the ambient temperature fluctuations. The artificial nest provided little insulation against temperature extremes, being warmer and cooler than the maximum and minimum local ambient temperatures, respectively. Nest cavity temperature was not found to have an influence on the breeding success of the southern ground-hornbill groups investigated in this study. These results have potentially important implications for southern ground-hornbill conservation and artificial nest design, as they suggest that the birds can tolerate greater nest cavity temperature extremes than previously thought.

Patterns of roost site selection and use by Southern Ground-Hornbills in north-eastern South Africa

Different habitats may be used for the needs of various aspects of an animal’s life. Southern Ground-Hornbill Bucorvus leadbeateri groups announce their presence within year-round territories by calling at dawn from their overnight roost sites. Knowledge on ground-hornbill roosting habits is limited. Groups roost in large trees, apparently close to where they end up after daily foraging. We investigated patterns of roost site selection and use for four Southern Ground-Hornbill groups in the Associated Private Nature Reserves, north-eastern South Africa, based on data from GPS-satellite transmitters. The number of roost sites used per month averaged 15.4 ± 4.7 across all groups, indicating little evidence of strong preferences for specific sites. This number was least when groups were breeding, decreasing throughout the early wet season (October–December) and was lowest during the late wet season (January–March) when actively breeding groups frequently roosted close to the nest (54–83% of roosts <1 000 m of the nest). As might be expected, the mean monthly number of nights per roost peaked during the breeding season (December–January). Riparian habitats were preferred for roosting during the breeding season, whereas disturbed areas, as well as Combretumand mopane-dominated habitats were preferred during the dry non-breeding season. Adequate large trees not only for nesting, but also for roosting, particularly in riparian habitats, may therefore be an important and potentially limiting factor for the successful reproduction of Southern Ground-Hornbills.

Seasonal changes in movement and habitat use by Southern Ground-Hornbills in the South African lowveld

Southern Ground-Hornbills Bucorvus leadbeateri are Endangered in South Africa and there is a concerted effort to reverse their population decline. They live in groups year round, with only the alpha pair breeding, raising at most one chick per year. Each group has a home range of 50–100 km2, but there are few data for their spatial habitat use within this range. Understanding the factors affecting Southern Ground-Hornbill movement patterns is useful to assess habitat management options for the species, to select sites for artificial nests and to identify suitable areas for reintroduction initiatives. We report daily and seasonal patterns of habitat use by four groups in the Associated Private Nature Reserves, north-east South Africa, based on data from GPS-satellite tags. Daily travel distances averaged 7.4 ± 2.2 km d−1 but were greater during the breeding season, although birds were constrained to forage close to their nest, and were lower in winter, when birds ranged more widely. Hourly travel distances were affected by time of day, season, temperature and group. Birds travelled farthest per hour in the morning, decreasing in the afternoon in winter. However, in summer hourly travel distances were bimodally distributed, with a minimum during the middle of the day when ambient temperatures exceed 25 °C. Acacia-dominated vegetation and riparian habitats were favoured disproportionately during the heat of the day in summer, presumably because they offer more shade than other habitats. Optimal habitat configurations for ground-hornbills include a mosaic of habitat types, including open areas for foraging and dense trees for shade.

Polybrominated diphenyl ethers (PBDEs) in eggshells of the Southern Ground-Hornbill (Bucorvus leadbeateri) and Wattled Crane (Bugeranus carunculatus) in South Africa

This study was undertaken to assess the levels of eight PBDE congeners, namely: PBDE-17, 47, 100, 99, 154, 153, 183 and 209 in eggshells of Southern Ground-Hornbill (SGH) Bucorvus leadbeateri and Wattled Crane (WC) Bugeranus carunculatus obtained from different nesting sites within the eastern savanna of Limpopo Province and the midlands of KwaZulu-Natal, respectively. Analyses were performed using gas chromatography–mass spectrometry employing the electron impact ionization technique. The results obtained indicated that the lower brominated congeners were predominant in both species. The total PBDEs ranged between not detected (ND) to 264μgg−1 lipid weight and 5.98–7146μgg−1 lipid weight in the SGH and WC samples, respectively. More so, the mean recoveries of the 13C-labelled surrogate standards ranged between 40% (PBDE-100) and 136% (PBDE-99). The potential hazards to these birds via PBDEs exposure were evaluated by determining the hazard quotients (HQs) by employing the established Lowest Observed Effect Level (LOEL) values associated with impaired pipping and hatching success as well as that associated with impaired reproduction. HQs values varying from 0.58 to 0.94 and 27.71 to 45.27, respectively were obtained for SGH and WC species. This implies that the SGH populations are exposed to low to moderate hazards, while the WC populations are susceptible to high hazards. Considering the potential threats posed by PBDEs, particularly to the WC species, it is likely that exposure to the current environmental levels of PBDEs by these birds may contribute to their reduced breeding success and declining population trends.

Egg-capping in the Southern Ground-Hornbill Bucorvus leadbeateri

‘Egg-capping’ describes occurrences of the empty shell from a hatched egg slipping over an unhatched egg from the same clutch. It is a rare phenomenon, occurring typically in <2% of nests monitored. Here I report the first two observed cases of egg-capping in the endangered Southern Ground-Hornbill Bucorvus leadbeateri. In north-eastern South Africa, egg-capping occurred in 4.3% of nests that contained two eggs with one or more surviving to hatching.

Developing a site selection tool to assist reintroduction efforts for the Southern Ground-Hornbill Bucorvus leadbeateri

The Southern Ground-Hornbill Bucorvus leadbeateri (SGH) is regarded as Vulnerable globally and Endangered in South Africa as a result of losing close to 70% of its range and 50% of its historic population in the country. One of the conservation tools being used to address this issue and restore the population to its historic range is reintroductions. The aim of this study was to identify and prioritise probable reintroduction sites in the Mopane Bioregion and the Limpopo and Mpumalanga sections of the Lowveld Bioregion of South Africa (all in the Savanna Biome), by using a niche-based modelling technique (Maxent) combined with GIS analyses. Suitable SGH habitat was determined for farms in the study area and evaluated for the absence of mappable threats. Three priority areas were identified for reintroductions. These areas are in a near-natural state, offer sufficient habitat, are free of mappable threats and are close to formally protected areas. Field surveys of these three priority areas are needed next to validate their suitability for reintroduction purposes. This is the first spatially explicit reintroduction plan for the SGH that has been developed and will contribute to conservationists’ efforts to conserve the SGH.

Random time-activity budgets in captive Southern Ground Hornbill Bucorvus leadbeateri

Introduction: The conservation status of the Southern Ground Hornbill (Bucorvus leadbeateri) is vulnerable on the IUCN Red List. The Mabula Ground Hornbill Conservation Project (2011) and Southern Ground Hornbill conservation in general aim to increase the number of hornbills through five main techniques: (1) supplemental feeding, (2) double clutching, (3) alternation of chicks, (4) group augmentation and (5) chick fostering. Numbers are threatened directly by habitat loss, hunting and international trade, and indirectly by group size (through the Allee effect) and communal breeding. Furthermore, the species has a highly K-selected life-history pattern. Captive breeding of this bird can potentially increase the population size twofold because both eggs laid are guaranteed a chance of survival, whereas in the wild only one egg is likely to survive. Time-activity budgets in birds can be used to illustrate reproductive effort. Time-activity budgets are known for Southern Ground Hornbills from wild birds in the Kruger National Park and from one captive pair (Johnson B 2004, personal communication). We compared the time-activity budgets of captive Southern Ground Hornbills in the Johannesburg Zoo with randomly expected behaviour of the same birds and previously studied birds.

Random time-activity budgets in captive Southern Ground Hornbill Bucorvus leadbeateri

Introduction: The conservation status of the Southern Ground Hornbill (Bucorvus leadbeateri) is vulnerable on the IUCN Red List. The Mabula Ground Hornbill Conservation Project (2011) and Southern Ground Hornbill conservation in general aim to increase the number of hornbills through five main techniques: (1) supplemental feeding, (2) double clutching, (3) alternation of chicks, (4) group augmentation and (5) chick fostering. Numbers are threatened directly by habitat loss, hunting and international trade, and indirectly by group size (through the Allee effect) and communal breeding. Furthermore, the species has a highly K-selected life-history pattern. Captive breeding of this bird can potentially increase the population size twofold because both eggs laid are guaranteed a chance of survival, whereas in the wild only one egg is likely to survive. Time-activity budgets in birds can be used to illustrate reproductive effort. Time-activity budgets are known for Southern Ground Hornbills from wild birds in the Kruger National Park and from one captive pair (Johnson B 2004, personal communication). We compared the time-activity budgets of captive Southern Ground Hornbills in the Johannesburg Zoo with randomly expected behaviour of the same birds and previously studied birds.

Causes of variable reproductive performance by Southern Ground-hornbillBucorvus leadbeateriand implications for management

Range occupancy of the cooperatively breeding Southern Ground-Hornbill Bucorvus leadbeateri in South Africa has decreased by 65% in the last three generations and the effective management of the remaining populations is hampered by a lack of fundamental understanding of the factors determining reproductive performance. We examined the influence of social and environmental factors on the species' reproductive success in South Africa using data gathered from 23 groups over eight breeding seasons. Some groups had access to artificial nest-sites, others did not. High rainfall (> 500 mm) over the breeding season led to a decrease in reproductive success, with groups being most successful in years when rain in the vicinity of the nest ranged from 300 to 500 mm. Groups breeding in natural nests were successful only when the proportion of open woodland surrounding the nest-site was high. Those that bred in artificial nests, where overall breeding success was more than twice as high as those in natural nests, were less dependent on the availability of open woodland. Large groups (more than three birds) bred more successfully than groups comprising only two to three individuals. Group size, helper effects and rainfall cannot be managed to increase the productivity of Ground-Hornbills but the fact that the availability of artificial nest-sites and the amount of open woodland around the nest-site both contribute positively to breeding performance identifies practical and simple management options for increasing the reproductive output of Southern Ground-Hornbill populations.

Breeding biology of Southern Ground Hornbill Bucorvus leadbeateri in Zimbabwe: impacts of human activities

This paper summarizes current knowledge and outlines future work on the breeding biology of Southern Ground Hornbill Bucorvus leadbeateri in Zimbabwe. All available records since 1900 were analysed, including casual reports by members of BirdLife Zimbabwe and published records. Estimates were made for the start and end of the breeding season, group sizes, clutch size and productivity levels, together with an assessment of preferred habitats and nest-tree species. There is a need for intensive fieldwork to determine aspects of breeding biology such as incubation and nestling periods. Particularly important for sound management and conservation strategies is relative breeding success in different land-tenure systems. The author has started work in a communal area 40 km south of Bulawayo city; land-use systems such as new resettlement areas, commercial farms and protected areas remain to be studied.

Visual fields in hornbills: precision‐grasping and sunshades

Retinal visual fields were determined in Southern Ground Hornbills Bucorvus leadbeateri and Southern Yellow‐billed Hornbills Tockus leucomelas (Coraciiformes, Bucerotidae) using an ophthalmoscopic reflex technique. In both species the binocular field is relatively long and narrow with a maximum width of 30° occurring 40° above the bill. The bill tip projects into the lower half of the binocular field. This frontal visual field topography exhibits a number of key features that are also found in other terrestrial birds. This supports the hypothesis that avian visual fields are of three principal types that are correlated with the degree to which vision is employed when taking food items, rather than with phylogeny. However, unlike other species studied to date, in both hornbill species the bill intrudes into the binocular field. This intrusion of the bill restricts the width of the binocular field but allows the birds to view their own bill tips. It is suggested that this is associated with the precision‐grasping feeding technique of hornbills. This involves forceps‐like grasping and manipulation of items in the tips of the large decurved bill. The two hornbill species differ in the extent of the blind area perpendicularly above the head. Interspecific comparison shows that eye size and the width of the blind area above the head are significantly correlated. The limit of the upper visual field in hornbills is viewed through the long lash‐like feathers of the upper lids and these appear to be used as a sunshade mechanism. In Ground Hornbills eye movements are non‐conjugate and have sufficient amplitude (30–40°) to abolish the frontal binocular field and to produce markedly asymmetric visual field configurations.